Current manufacturing processes rely on the efficient assembly of parts to create products in a wide variety of industries. To facilitate this assembly of parts, repetitive operations are identified and automated where possible. For instance, welding operations are automated where identical parts are welded to identical pieces or assemblies during the manufacturing process. In some instances, the identical parts are selected, placed, and held to the assembly by one or more devices that automate these repetitive tasks.
Many of these devices use fluid cylinders to perform the repetitive tasks. Such fluid cylinders include hydraulic cylinders and pneumatic cylinders. Pneumatic cylinders typically include a piston and a rod within a housing moved by the force of pressurized air. In some cases, a tool is attached to the rod which is moved axially through the cylinder towards a bin containing parts. The tool includes an interface which interacts or mates with the part. This interface can include, for instance, a magnetic interface, a vacuum interface, or fitted interface. The interface is moved to the bin through the application of air to the cylinder. The part is selected and removed from the bin and then moved to the assembly being manufactured.
Pneumatic cylinders are known to include a cylinder housing, a rod, and an actuating piston. The rod moves between extended and retracted positions relative to the cylinder housing which includes a longitudinal axis and an outer surface. The actuation piston, which is coupled to the rod, moves the rod between the extended and retracted positions upon the application of air pressure to one or more air ports.
It is also known for a pneumatic cylinder to include a cylinder housing with a rod cover and a head cover. The head cover, located at one end of the pneumatic cylinder, includes an extend air port for directing pressurized air to the interior of the cylinder. A rod cover, located at an opposite end of the cylinder cover, includes a retract air port and an aperture to receive a rod assembly. The rod assembly includes an outer rod and an inner rod located within a channel of the outer rod. During operation, application of pressurized air to the extend air port, moves the outer rod in the longitudinal direction to extend the outer rod from the cylinder housing. Upon further application of air pressure to the extend pressure port, the inner rod moves within the channel of the outer rod, such that the inner piston rod extends from a stationary outer rod. Typically, a tool is coupled to the inner rod to select a part for the manufacturing operation. Once selected, the air pressure is removed from the extend pressure port and applied to the retract pressure port. The inner rod moves into the outer rod and the selected part is removed from the tool through contact with the outer rod. In some cases, the outer rod may press the part into place.
The outer rod is coupled to a first piston located within the cylinder housing. An outer surface of the first piston contacts an inner surface of the cylinder housing and moves in the longitudinal direction upon application of air pressure to the extend air pressure port. The inner rod is coupled to a second piston located within a cavity of the first piston. The second piston is contained within the cavity of the first piston during its entire travel. The second piston also includes push back pins which extend through the first piston and contact the rod cover. Pressurized air, passing through the extend pressure port, is directed to both the first and second piston at the same time. The outer rod continues to move with respect to the inner rod once the push back pins contact the rod cover. This movement of the outer rod with respect to the inner rod, removes the part from the tool and in some cases pushes the part to a desired location.
Because the second piston is located within the first piston at all times and the extend pressure port is open to both pistons, the breakaway force of the first piston with respect to the cylinder and the breakaway force of the second piston with respect to the first piston are selected to be different. A first piston seal of the first piston includes a first breakaway force between the cylinder and the first piston. A second piston seal of the second piston includes a second breakaway force between the second piston and the cavity of the first piston. The first piston seal force is adjusted to be less than the second piston seal force so that the inner piston can move independently of the outer piston.